This invention relates to an inexpensive method to manufacture carbonate ester. More particularly, it relates to a method whereby carbonate ester is obtained by the metal induced reaction of a hydroxy compound with a sulfur compound.
Polycarbonate can be made by interfacial reaction or melt transesterification. The melt transesterification of a carbonate ester provides an environmental advantage over the reaction of hydroxy compounds, such as bisphenols, with phosgene under interfacial reaction conditions. In addition, polycarbonates prepared by melt transesterification have low levels of contaminants, such as sodium and halide ions. This makes these materials particularly suitable for use in optical applications, such as the manufacture of compact disks.
Because of the benefits, there is an interest in the manufacture of polycarbonates by melt transesterification of carbonate esters. However, before it can be extensively exploited on a commercial scale, a satisfactory manufacturing method for the carbonate ester must be developed.
The prior art includes three potential commercial routes for the preparation of carbonate ester: direct phosgenation of a phenol in an organic medium; a multi-step, low conversion melt transesterification of dialkyl carbonate with a phenol using a catalyst such as a titanium compound; and the direct carbonylation of a phenol requiring a catalyst, for example Pd, that is difficult to recycle.
The present invention further provides a method of producing orthocarbonate which can be converted into carbonate ester in a subsequent operation. Methods to produce orthocarbonate have been disclosed in the prior art. Typically, these methods required the use of organic halides with a base. Trace amounts of carbonate ester have also been generated. These prior art methods typically utilize a procedure with a number of incremental steps wherein a cuprous phenoxide species is presynthesized and then combined with carbon disulfide in an organic solvent.